CN111699262A

CN111699262A - Process for the production of esters and biolubricants catalysed by fermented solids

Info

Publication number: CN111699262A
Application number: CN201880074449.9A
Authority: CN
Inventors: J·A·卡瓦坎蒂达席尔瓦; G·B·圭拉; D·M·吉马良斯弗莱雷; E·C·冈卡维斯圭亚那; E·D·卡瓦坎蒂奥利维亚; J·格力高杜阿特; K·L·伊格纳西奥; V·F·索尔里斯; P·R·达席尔瓦
Original assignee: University Rio De Janeiro; Petroleo Brasileiro SA Petrobras
Current assignee: University Rio De Janeiro; Petroleo Brasileiro SA Petrobras
Priority date: 2017-10-20
Filing date: 2018-10-11
Publication date: 2020-09-22
Anticipated expiration: 2038-10-11
Also published as: AU2018351874B2; WO2019077313A1; BR102017022583A8; CN111699262B; US20210189442A1; BR102017022583A2; JP2021500074A; CA3079556A1; US11866761B2; JP7323895B2; AU2018351874A1

Abstract

The present invention relates to a method for producing an ester, which comprises reacting methyl biodiesel or free fatty acids with a polyhydroxylated alcohol in the presence of a biocatalyst, which is a fermented solid containing Rhizomucor miehei lipase produced by culturing microorganisms on agricultural waste by solid state fermentation.

Description

Process for the production of esters and biolubricants catalysed by fermented solids

Technical Field

The present invention relates to the field of biocatalysis. More specifically, the present invention relates to the development of a new biocatalytic route that extends the possibility of obtaining esters that can be used as biolubricants by enzymatic routes.

Background

Base oils are the major constituent of lubricating oils and can be classified as mineral (obtained by distillation and refining of petroleum) and synthetic (obtained on the basis of chemical reactions of materials coming from the petrochemical industry.) although only a small portion of petroleum is consumed in the production of lubricants, a high percentage of these products is not properly discarded and therefore constitutes a threat to the environment⁶And (5) lifting water.

Increasingly stringent requirements imposed by environmental legislation, as enforced by european standard EN 13432, the demand in certain countries for food-grade lubricants for industry in this field and the problem of limited availability of petrochemical resources have helped to develop products derived from alternative sources and constitute one of the main priorities in the field of petrochemistry.

Biolubricants are biodegradable lubricants which can be broken down by microbial action and are generally obtained from vegetable oils modified by chemical reactions and used in applications where the possibility of leakage can jeopardize the environment.

Generally, biodegradability refers to the tendency of a lubricant to be metabolized by microorganisms for a period of up to one year. The form in which the microorganisms cause decomposition depends essentially on their structure. Vegetable oils are typically 99% biodegradable, usually falling to 90% -98% after mixing with additives.

The main types of esters used as biolubricants are diesters, phthalates, trimellitates, C36 dimers and polyol esters. Polyol esters are produced in the reaction between a polyol and a monocarboxylic or dicarboxylic acid. Such products offer unusual stability due to the absence of para-hydrogen in the beta position and the presence of a central quaternary carbon atom.

The reactions employed in the production of esters useful as biolubricants catalyzed by chemical catalysts are known in the art.

Document BR1020130335827 describes the production of a biolubricant based on the exchange reaction of biodiesel from castor oil with trimethylolpropane esters catalyzed by dibutyltin dilaurate (DBTDL). It should be noted that the reaction conditions are severe when DBTDL is used, requiring temperatures between 168 ℃ and 172 ℃ and vacuum.

Enzymatic or biological catalysts offer various advantages over chemical catalysts. These advantages include, for example, high selectivity of enzymes to their substrates, high yield, milder reaction conditions such as temperature and pressure, no degradation of the equipment, and biodegradability of the biocatalyst.

However, the high cost of commercially available enzyme preparations has been an obstacle to their economic viability for industrial application in the synthesis of low value-added and high-volume-sold products.

The use of enzymes in the solid form of a fermentation produced by solid state fermentation represents an alternative to reducing production costs, since the enzyme extraction and purification steps are eliminated.

Patent document PI0704791-6 relates to a process for synthesizing esters for use as biodiesel, which employs a reaction catalyzed by a fermented, solid-form lipase produced by the solid state fermentation of the bacterium Burkholderia cepacia (Burkholderia cepacian).

In the process of said prior art document, a fatty acid (in the case of an esterification reaction) or a triglyceride source (in the case of a transesterification reaction) is reacted with a monohydroxylated alcohol, which is preferably ethanol. This document does not envisage transesterification and hydroesterification reactions with polyhydroxylated alcohols, except for the use of enzymes of bacterial origin.

To date, it can be concluded that there has not been described in the prior art a method for obtaining biolubricant esters using transesterification and hydroesterification reactions with polyhydroxylated alcohols catalyzed by fermented solids obtained by culturing microorganisms on agricultural waste.

The present invention includes the use of low cost lipases, which facilitate the utilization of biomass and the economic feasibility of producing biolubricants by enzymatic routes.

Summary of The Invention

It is an object of the present invention to provide a process for producing esters which solves the above-mentioned main problems of the prior art.

To achieve the object, the present invention provides a method for producing an ester, which comprises reacting methyl biodiesel or Free Fatty Acids (FFA) with polyhydroxylated alcohols in the presence of a biocatalyst, wherein the biocatalyst is a fermented solid produced by culturing microorganisms in agricultural waste by solid state fermentation.

Another object of the invention relates to the use of the produced esters as biolubricants.

Another object of the invention relates to a biolubricant comprising the ester produced by the process of the invention.

Drawings

Fig. 1 shows the synthesis of a bio-lubricant based on the reaction between soy biodiesel and neopentyl glycol catalyzed by rhizomucor miehei (r.miehei) lipase present in the fermented solids of palm oil cake.

Fig. 2 shows the re-use of the fermented solids of palm oil cake in the synthesis of a bio-lubricant based on the reaction between soybean biodiesel and neopentyl glycol.

Fig. 3 shows the synthesis of a bio-lubricant based on the reaction between castor oil biodiesel and trimethylolpropane catalyzed by rhizomucor miehei (r. miehei) lipase present in the fermented solids of palm oil cake.

Fig. 4 shows the synthesis of a bio-lubricant based on the reaction between castor oil biodiesel and neopentyl glycol catalyzed by rhizomucor miehei (r.miehei) lipase present in the fermented solids of cottonseed oil cake.

Fig. 5 shows the synthesis of a bio-lubricant based on the reaction between free fatty acids of castor oil and neopentyl glycol catalyzed by rhizomucor miehei (r.miehei) lipase present in the fermented solids of cottonseed oil cake.

Fig. 6 shows the synthesis of a bio-lubricant based on the reaction between free fatty acids of soybean and neopentyl glycol catalyzed by rhizomucor miehei (r.miehei) lipase present in the fermented solids of cottonseed oil cake.

Fig. 7 shows the activity of the fermented solids of palm oil cake (SEP) after several re-uses without solvent washing in the bio-lubricant synthesis.

Detailed Description

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the subject matter of this invention belongs. The terminology used in the description of the invention has been for the purpose of describing particular embodiments only and is not intended to limit the scope of the teachings. Unless otherwise indicated, all numbers expressing quantities, percentages and proportions, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term "about". Accordingly, unless otherwise indicated, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties to be obtained.

The present inventors have solved the problems of the prior art by providing a method for producing esters comprising reacting methyl biodiesel or free fatty acids with a polyhydroxylated alcohol in the presence of a biocatalyst, wherein the biocatalyst is a fermented solid produced by culturing microorganisms in agricultural waste by solid state fermentation.

In a first aspect, the invention includes producing a low cost lipase for use in the synthesis of biolubricant esters. For this purpose, agricultural waste is used as culture medium in solid state fermentation processes.

Solid state fermentation makes it possible to use low cost raw materials as culture media for microorganisms, with a single fermentation medium. In this method, the substrate not only provides nutrients for culturing the microorganisms, but also serves as a carrier for cell growth.

In the context of the present invention, the term "agricultural waste or waste materials" is understood to mean the solid residue (cake) of the oily raw material. Preferably, solid residues from palm oil and cottonseed oil extraction are used.

The term "inoculum" is understood as the cells of the microorganism in the form of spores or plant cells which are used to initiate the fermentation process. Preferably, the microorganism is a filamentous fungus. More preferably, the fungus is of the genus rhizomucor. Even more preferably, the fungus is a Rhizomucor miehei (Rhizomucor miehei) species.

The term "fermenter" is understood as a chamber with controlled temperature and humidity for growing microorganisms on the cake.

The term "fermented solids" is understood as dry fermented cake at the end of the solid state fermentation process, which contains biomass of microorganisms and lipases.

In one embodiment, water is added to the solid state fermentation based palm oil cake or cotton seed oil cake in a ratio that is ideal for the fermentation process, and then mixed into the inoculum.

The wetted and inoculated cake is then incubated in a fermenter during which the microorganism grows and, as a result of its metabolism, produces a group of lipases with high synthesis capacity.

At the end of the solid state fermentation, the fermented cake is subjected to a drying step and then used for catalytic reactions. Preferably, drying is carried out by lyophilization or forced air.

A low cost enzymatic biocatalyst produced by a solid state fermentation process is used in a transesterification or hydroesterification reaction to produce a biolubricant ester.

In the transesterification process, methyl biodiesel is reacted with a polyhydroxylated alcohol to produce a biolubricant ester. Preferably, the methyl biodiesel is soy methyl biodiesel or castor oil methyl biodiesel. Preferably, the polyhydroxylated alcohol is neopentyl glycol, trimethylolpropane or pentaerythritol.

In one embodiment, the transesterification reaction is conducted with a biodiesel to alcohol molar ratio of 2 to 5 and optionally 1 to 3% (w/w) water. The fermented solids were used as biocatalyst at a concentration of 10-30% (w/w). The reaction is carried out in a reactor at a temperature of 30-50 ℃ and under stirring at atmospheric pressure.

In a preferred embodiment, the reactor used is a stirred tank at atmospheric pressure with controlled temperature in which the transesterification reaction is carried out.

Under these conditions, the methyl ester undergoes transesterification with an alcohol to produce a biolubricant ester and methanol as a by-product. The product is isolated at the end of the process.

The hydroesterification process consists of a first hydrolysis reaction and a second esterification reaction.

In one embodiment, the first reaction (hydrolysis) comprises mixing the oil containing oil and the buffer in a volume ratio of 1:1, followed by addition of the lipase in a proportion of 1-2% w/v of the weight of the oil.

The reaction is carried out in a reactor at a temperature of 30-40 ℃ and atmospheric pressure with stirring. In these conditions, the oil is hydrolysed and free fatty acids and glycerol are produced as by-products. The free fatty acids are separated from the buffer, glycerol and lipase prior to use in the esterification reaction.

In a preferred embodiment, the oil-containing oil is soybean oil or castor oil and the lipase is a commercial lipase from Candida rugosa (Candida rugosa) or a lipase obtained from dormant castor oil plant seeds.

In a preferred embodiment, the reactor used is a temperature-controlled stirred tank at atmospheric pressure, in which the hydrolysis reaction is carried out.

In one embodiment, the second reaction (esterification) is carried out by reacting the free fatty acid and the polyhydroxylated polyol with water in a free fatty acid to alcohol molar ratio of 2 to 5 and optionally 1 to 3% (w/w). The fermented solids were used as biocatalyst at a concentration of 10-30% (w/w). The reaction is carried out in a reactor at a temperature of 30-50 ℃ and atmospheric pressure with stirring.

In a preferred embodiment, the reactor used is a stirred tank at atmospheric pressure with controlled temperature in which the esterification reaction is carried out.

In these conditions, the free fatty acid is esterified with a polyol to produce a biolubricant ester and water as a by-product.

The biolubricant esters obtained by the process of the present invention were analysed with respect to their physicochemical properties, which showed satisfactory physicochemical characteristics consistent with those of currently available biolubricants.

The viscosity of the biolubricant is the most important property of these fluids, as it is directly related to the formation of a film that will protect the metal surface against erosion.

The viscosity index is a parameter of the oil viscosity behavior at temperature. The higher the value, the less the change in oil viscosity with temperature. In general, the value of the viscosity index is determined by a calculation that takes into account the viscosity of the product at 40 ℃ and 100 ℃.

The flow point measures the lowest temperature at which the oil still flows and is the test used to evaluate the behavior of a lubricating oil when subjected to low temperatures.

The physical and chemical properties of the biolubricants such as viscosity, viscosity index and flow point are higher than those of mineral-based lubricants.

The properties and performance of the biological lubricant of the present invention can be further improved by using additives that are compatible with the lubricant and preferably that are non-toxic and biodegradable.

The esters produced by the process of the invention are particularly useful in lubricating applications where the maximum operating temperature is below 120 ℃, but where the ambient temperature remains above-40 ℃.

The biological lubricant of the present invention can be used as engine oil, pressure transmission liquid, rolling liquid, and the like.

The invention will be further illustrated by the following examples which are not to be considered as limiting. As will be apparent to those skilled in the art, the present invention is not limited to these specific embodiments.

Examples

Example 1 production of fermented solid

The fermented solid of Rhizomucor miehei (Rhizomucor miehei) was obtained as a result of the fermentation of cottonseed oil cake (crushed) or palm oil cake (crushed and sieved, particles less than 1.18 mm). The fermentation was carried out in a beaker containing 15g of cake and the water content was adjusted to 65% and 50% for the palm oil cake and the cotton seed oil cake, respectively. Each beaker containing the cake was sterilized in an autoclave at 121 ℃ for 15 minutes, and the cake was sterilized at 10 ℃⁷One Rhizomucor miehei spore/gram of solid (dry weight) was inoculated and incubated at 30 ℃ for 72h in a climatic chamber at a relative humidity of 90%. At the end of the fermentation, the fermented medium was lyophilized and stored at 4 ℃ until use. The fermented solid of Mucor miehei is obtained by solid state fermentation using palm oil cake or cottonseed oil cake as raw material, and the hydrolytic activity is 17 + -2U/g and 29 + -1U/g, respectively.

Example 2 hydrolytic Activity

The hydrolytic activity of the fermented solid was estimated from the change in absorbance in spectrophotometry, which was facilitated by hydrolysis of basal p-nitrophenyl laurate (p-NFL) at a concentration of 25mM in a solution of acetonitrile/dimethyl sulfoxide (DMSO)1: 1. For the hydrolysis reaction of the substrate, an aliquot of 250 μ Ι _ of p-NFL solution was diluted in 2.2mL of sodium phosphate buffer pH 7.0(25mM) in a chamber, which was acclimatized at 30 ℃ for 2 minutes. After this time, 50 μ L aliquots of the liquid enzymatic extract were added and the absorbance was monitored at 412nm in a spectrophotometer (SHIMADZU UV-1800). 1 enzyme unit (U) corresponds to the amount of enzyme capable of producing 1. mu. mol of p-nitrophenol per minute in the test conditions. Activity was calculated using equation 1:

wherein:

α ═ the change in absorbance (Δ absorbance) in the elapsed time interval Δ t (in minutes) during the phase of linear increase in absorbance;

d ═ dilution of enzyme solution;

f ═ conversion factor (0.094 μmol^-1) Which is prepared by constructing the concentration of 0.01-0.2 mu mol^-1A standard curve of p-NFL varying in between;

vf ═ reaction volume, which is the volume of p-NFL solution in buffer and sample volume (mL);

vs — volume of enzyme solution used in the test (mL).

The hydrolytic activity (U/g) expressed per gram of dry cake was calculated by equation 2:

wherein:

vt ═ volume of buffer used in the extraction enzyme;

and m is the dry weight of the cake.

Example 3 transesterification

Example 3.1-Soy biodiesel and neopentyl glycol

The reaction between soybean biodiesel and neopentyl glycol gave the product at 85.5% conversion after 48h of the solid catalyzed reaction of fermentation of rhizomucor miehei (r.miehei) produced on palm oil cake.

The reaction of soy biodiesel with neopentyl glycol was carried out with stirring at atmospheric pressure, with a molar ratio of alcohol/biodiesel from 2:1 to 3.1:1, a biocatalyst from 10 to 30% (w/w) and a water content from 1 to 2.5% (w/w) and a temperature from 35 to 50 ℃ (fig. 1).

The product of the reaction between soybean biodiesel and neopentyl glycol catalyzed by the fermented solid lipase of palm oil cake was produced in a considerable volume (200ml) and characterized to determine the properties of the produced biolubricant (table 1). All other properties evaluated were satisfactory except for the acidity index.

Table 1: the reaction between soybean biodiesel and neopentyl glycol produces a biolubricant characteristic.

Test results
	Moisture (ppm)884.4
Viscosity 100 deg.C (mm)²/s)4.290
	Viscosity 40 deg.C (mm)²/s)15.41
Viscosity index 206
	Fluidity (. degree. C.) -6
Acidity index (mgKOH/g)19.8
	Rotary pump (min)30

The solids of the fermentation of the palm oil cake were evaluated in terms of reuse in the reaction between soybean biodiesel and neopentyl glycol. After a reaction time of 24h or 72h, the enzyme was washed with solvent (hexane or ethanol), followed by filtration in a buchner funnel and incubation in a desiccator overnight. At the end of this procedure, the enzyme was used again in the reaction described in example 1. The fermented solids of the palm oil cake can be used again at least once after washing with hexane or ethanol (fig. 2). Reuse without solvent washing was also tested. In this case, after 72h of reaction, the product was removed at the top of the reactor after decanting the fermented solids. Fresh reaction medium was then added to the reactor in a weight equal to the weight of the withdrawn product (figure 7).

Example 3.2 Castor oil biodiesel and alcohols trimethylolpropane and pentaerythritol

The reaction between castor oil biodiesel and the alcohols trimethylolpropane and pentaerythritol, respectively, gave the product in 72h with a conversion of 52%. The reaction was carried out using fermented solids of rhizomucor miehei (r.miehei) produced on palm oil cake as biocatalyst.

The reaction between castor oil biodiesel and the alcohols trimethylolpropane and pentaerythritol was carried out at a molar ratio of 2-3.75:1 alcohol/biodiesel, 10-30% (w/w) of biocatalyst, and with a water content of 1-3% (w/w) and a temperature of 30-50 ℃, under stirring at atmospheric pressure (fig. 3).

Example 3.3 Castor oil biodiesel and neopentyl glycol

The reaction between castor oil biodiesel and neopentyl glycol gave the product in 96h at 91% conversion. The reaction is carried out using the fermented solid of rhizomucor miehei produced on the cottonseed oil cake as a biocatalyst.

The reaction between castor oil biodiesel and neopentyl glycol was carried out at a molar ratio 2-4:1 alcohol/biodiesel, 10-30% (w/w) of biocatalyst, and with a water content of 1-3% (w/w) and a temperature of 30-50 ℃, under stirring and at atmospheric pressure (fig. 4).

The product of the reaction between castor oil biodiesel and neopentyl glycol catalyzed by the fermented solid lipase of palm oil cake was produced in a considerable volume (200ml) and characterized to determine the properties of the produced biolubricant (table 2). In addition to the acidity index, other properties are satisfactory.

Table 2: the reaction between castor oil biodiesel and neopentyl glycol produces a biolubricant characteristic.

The solids of the fermentation of the cottonseed oil cake were evaluated for reuse in the reaction between castor oil biodiesel and neopentyl glycol. After a reaction time of 24h, the enzyme was washed with solvent (ether or ethanol), followed by filtration in a buchner funnel and incubation in a desiccator overnight. At the end of this procedure, the enzyme is used again in the above reaction. The cotton SEP can be reused at least once after washing with ether or ethanol.

Example 4 hydrogenation esterification

Example 4.1 Free Fatty Acids (FFA) and neopentyl glycol of Castor oil

The reaction between FFA and neopentyl glycol of castor oil gave the product in 96h with 65% conversion. The reaction was carried out using the fermented solids of rhizomucor miehei (r. miehei) produced on cottonseed oil cake as biocatalyst.

The reaction of FFA of castor oil with neopentyl glycol was carried out at a molar ratio of 2-4:1 alcohol/FFA, 10-30% (w/w) biocatalyst, and with a water content of 1-3% (w/w) and a temperature of 30-50 ℃, under stirring at atmospheric pressure (fig. 5).

The product of the reaction between FFA and neopentyl glycol of castor oil catalyzed by the lipase of cotton SEP was produced in a considerable volume (200ml) and characterized to determine the properties of the produced biolubricant (table 3). All other properties evaluated were satisfactory except for the acidity index.

Table 3: the reaction between FFA and neopentyl glycol of castor oil produces the characteristics of a biolubricant.

Example 4.2 Soybean Free Fatty Acid (FFA) and neopentyl glycol

The reaction between soy FFA and neopentyl glycol gave the product in 72h with 82% conversion. The reaction was carried out using the fermented solids of rhizomucor miehei (r. miehei) produced on cottonseed oil cake as biocatalyst.

The reaction between soy FFA and neopentyl glycol was carried out at a molar ratio of 2-4:1 alcohol/FFA, 10-30% (w/w) of biocatalyst, and with a water content of 1-3% (w/w) and a temperature of 30-50 ℃, under stirring at atmospheric pressure (fig. 6).

The product of the reaction between soybean FFA and neopentyl glycol catalyzed by the lipase of cotton SEP was produced in a considerable volume (200mL) and characterized to determine the properties of the produced biolubricant (table 4). All other properties evaluated were satisfactory except acidity index, fluidity and moisture.

Table 4: the reaction between soy FFA and neopentyl glycol produces the characteristics of a biolubricant.

Test results
	Moisture (ppm)2150.3
Viscosity 100 deg.C (mm)²/s)20.27
	Viscosity 40 deg.C (mm)²/s)5.034
Viscosity index 191
	Fluidity (. degree. C.) 15
Acidity index (mgKOH/g)105.5
	Rotary pump (min)28
Rancidity apparatus (h)3.08

Example 5 determination of reaction acidity

The content of free fatty acids in the oil and product was determined by neutralization titration. The free fatty acid (about 0.2g of sample) was used at 0.04mol.L^-1The NaOH solution was titrated in a Mettler DG 20 brand autotitrator until pH 11.0 and the acidity of the sample was determined by equation 3.

Alternatively, for samples with larger volumes, free fatty acids from about 0.5-1g of sample are used with 0.25mol^-1The NaOH solution of (a) was titrated using phenolphthalein as an indicator, and the acidity of the sample was determined by equation 3.

Wherein:

v — volume of sodium hydroxide used in sample titration (mL);

molar concentration of M ═ NaOH solution (mol.l)^-1)；

AG — the molecular weight (g) of the fatty acid present in the oil at the highest concentration;

m is the sample weight (g).

Soy oil ═ linoleic acid (280 g); castor oil-ricinoleic acid (298 g).

EXAMPLE 6 determination of the methyl ester content

To determine the amount of methyl ester (biodiesel) in the transesterification reaction product, a 20 μ L aliquot was diluted in 480 μ L of n-heptane and injected into a chromatograph. A gas chromatograph (SHIMADZU 2010) equipped with a Flame Ionization Detector (FID) and an omega wax capillary column (length 30m, inner diameter 0.25mm and film thickness 0.25 μm) was used. The conditions of the analysis were: the initial temperature of 200 ℃ for 5 minutes, then programmed at a rate of 20 ℃/min up to 260 ℃, held at 260 ℃ for 6 minutes. The temperatures of the detector and syringe were 250 ℃ and 260 ℃, respectively. Helium at a flow rate of 2.0mL/min was used as the carrier gas and injection was done in a split mode of 1: 20. Methyl heptadecanoate was used as an internal standard and the ester content was calculated using equation 4.

Example 7 conversion in esterification reaction

Conversion of free fatty acids to the biolubricant was monitored by titration method (acidity) where FFA consumption was observed. The conversion rate of the reaction is calculated by equation 5 or equation 6.

The results from equation 5 are expressed as a percentage of esterified FFA, regardless of excess FFA in the reaction, so that 100% conversion is equivalent to 100% of the esterified alcohol's hydroxyl groups. The results from equation 6 are expressed as a percentage of esterified FFA such that 100% conversion is equivalent to 100% of esterified FFA.

Wherein:

A_iinitial acidity (% w/w);

A_ffinal acidity (% w/w);

RM ═ initial molar ratio FFA/alcohol;

number of hydroxyl groups in H ═ alcohol molecule

Example 8 conversion in transesterification

The conversion rate in the transesterification reaction is calculated by equation 7. The results are expressed as a percentage of transesterified biodiesel, regardless of the excess biodiesel and free fatty acids formed in the reaction, so that 100% conversion is equivalent to 100% of the hydroxyl groups of the alcohol being esterified.

Wherein:

ei ═ initial ester content (% w/w);

ef-final ester content (% w/w);

ai is initial acidity (% w/w);

af-final acidity (% w/w);

RM ═ initial molar ratio biodiesel/alcohol;

number of hydroxyl groups in H ═ alcohol molecule

It is clear that the above examples have been presented for illustrative purposes only and that modifications and variations thereto as would be apparent to persons skilled in the art are deemed to be within the scope of the invention as defined by the claims presented herein below.

Claims

1. A process for producing an ester, characterized in that the process comprises reacting methyl biodiesel or free fatty acids with a polyhydroxylated alcohol in the presence of a biocatalyst, wherein the biocatalyst is a fermented solid produced by culturing a microorganism on agricultural waste by solid state fermentation.

2. Process according to claim 1, characterized in that the reaction of the methyl biodiesel with the polyhydroxylated alcohol is a transesterification reaction.

3. Process according to claim 1, characterized in that the reaction of the free fatty acids with the polyhydroxylated alcohols is a hydroesterification reaction.

4. A process according to claim 1 or 2, characterized in that the biodiesel is soy biodiesel or castor oil biodiesel.

5. A process according to any one of claims 1 to 4, characterized in that the biocatalyst is used in a concentration of 10 to 30% by weight.

6. Process according to any one of claims 1 to 5, characterized in that a molar ratio of alcohol to methyl biodiesel or free fatty acids of 2:1 to 5:1 is used.

7. Process according to claim 1, characterized in that the free fatty acids are obtained by reacting soybean oil or castor oil with a biocatalyst.

8. Process according to claim 7, characterized in that the biocatalyst is one or more commercial lipases or one or more lipases obtained from dormant castor beans.

9. A process according to any one of claims 1 to 8, characterised in that the polyhydroxylated alcohol is neopentyl glycol, trimethylolpropane or pentaerythritol.

10. Method according to any one of claims 1 to 9, characterized in that the microorganism is a fungus.

11. The method according to claim 10, characterized in that the fungus is Rhizomucor miehei (Rhizomucor miehei).

12. A method according to any one of claims 1 to 11, characterised in that the agricultural waste is cottonseed cake or palm oil cake.

13. Process according to any one of claims 1 to 12, characterized in that the fermented solid is added to the reaction in the form of a lyophilisate.

14. Process according to any one of claims 1 to 13, characterized in that the fermented solids are reused at least once.

15. Process according to any one of claims 1 to 14, characterized in that it additionally comprises a step of purifying the ester produced.

16. Use of an ester produced by the process as defined in any one of claims 1 to 15, characterized in that the ester is used as a bio-lubricant.

17. A biolubricant characterised in that it comprises an ester produced by a process as defined in any one of claims 1 to 15.